1. Field of the Invention
This invention relates a two-stage columnar supercritical fluid fractionation process for deacidifying vegetable oils and enriching the oils in phytosterols and phytosterol esters.
2. Description of the Prior Art
Certain vegetable oils, such as rice bran oil (RBO) and corn fiber oil have been identified as sources rich in phytosterols and other nutraceuticals such as tocopherol and tocotrienols. Research studies have shown that these oils have potential health benefits, such as lowering plasma cholesterol levels (R. J. Nicolosi et al., Atherosclerosis, 88:133-142, 1991), and C. Rukmini et al., J. Am. Coll. Nutr., 10:593-601, 1991), decreasing early atherosclerosis (N. Rong et al., Lipids, 32:303-309, 197), and inhibiting platelet aggregation (G. S. Seetharamiah et al., J. Nutr. Sci and Vitaminol., 36:291-297, 1990).
The free fatty acid (FFA) content of rice bran may be as high as 30-40% (w/w), if the bran is not processed properly prior to extraction of the oil (B. K. De et al., J. Am. Oil Chem. Soc., 76(10):1243-1246, 1999). This is due to the lipolysis caused by the native lipase enzymes present in the bran. FFA present in the crude oils are not desired. They are removed from crude oil by alkali refining during industrial edible oil processing.
Conventional chemical and physical vegetable oil processing techniques have several disadvantages, including the use of large quantities of water and chemicals, generating large quantities of waste, as well as being energy intensive (V. Kale et al., J. Am. Oil Chem. Soc., 76(6):723-727, 1999). Furthermore, a significant portion of the nutritive rice bran oil components is lost during the conventional refining processes. According to Orthofer (P. Bondioli et al., J. Am. Oil Chem. Soc., 69(5):477-480, 1992), 50% of the rice bran oil phytosterols are lost during the refining process. Xu et al. (JAOCS, 2000, 77:547-551) compare supercritical fluid and solvent extraction methods in extracting y-oryzanol from rice bran.
Alternative deacidification processes such as methanol extraction of FFA followed by membrane processing (V. Kale et al., J. Am. Oil Chem. Soc., 76(6):723-727, 1999) and reesterification of rice bran FFA with monoglycerides (B. K. De et al., J. Am. Oil Chem. Soc., 76(10):1243-1246, 1999) have been reported. Supercritical fluid fractionation (SFF) techniques with supercritical carbon dioxide (SCxe2x80x94CO2) have been reported for deacidification of vegetable oils, including: refining of lampante oil (P. Bondioli et al., J. Am. Oil Chem. Soc., 69(5):477-480, 1992), and deacidification of roasted peanut (G. R. Ziegler et al., J. Am. Oil Chem. Soc., 70(10):947-953, 1993) and olive oil (L. Brunetti et al., J. Am. Oil Chem. Soc., 66(2):209-217, 1989). Recently, Dunford and King (N. T. Dunford et al., J. Food Sci. 65:1395-1399, 2000) have used a SFF tower approach to deacidify crude RBO and determined the optimal conditions for FFA removal, while minimizing phytosterol and triglyceride (TG) losses during the process. The fractionation tower utilized for this study was operated under isothermal conditions, however by applying a temperature gradient along the SFF tower, one may improve the purity of the extract by causing an internal reflux in the column (T. Clifford, Fundamentals of Supercritical Fluids, Oxford University Press Inc., New York, pp. 130-144, 1999).
Critical fluid processing can be used in several modes for producing nutraceutical ingredients or functional foods. Exhaustive extraction in which SCxe2x80x94CO2 or a SCxe2x80x94CO2-cosolvent mixture is used to yield an extract equivalent to those obtained with organic solvent extraction or pressing/expelling technologies (J. W. King et al., Supercritical Fluid Technology in Oil and Lipid Chemistry, AOCS Press, Champaign, Illinois, p. 435, 1996) and is well-documented in the recent literature (M. Mukhopadhyay, Natural Extracts Using Supercritical Carbon Dioxide, CRC Press, Bacon Raton, Florida, p. 339, 2000). Fractional extraction where extraction pressure, temperature, time, or the addition of a cosolvent is varied on an incremental basis, is also capable of producing extracts that are somewhat either enriched or depleted in the desired nutraceutical agents (J. W. King, Cosmet Toil., Vol. 61, p. 61, 1991). Such fluid density-based or cosolvent-assisted extractions frequently yield extracts with considerable extraneous material. Indeed specifically extracting or enriching a desired solute out of natural product matrix is somewhat complex and difficult due to the very low concentration levels of many of these agents.
To enrich the concentration of desired component(s), researchers have resorted to fractionation techniques utilizing critical fluids. One of the simplest is separation of the extract with the aid of multiple separators held at different combinations of temperatures and pressures (E. Reverchon, J. Supercrit. Fluids, Vol. 5, p. 256, 1992). Using such an approach, the fractionation of essential oils from waxes and oleoresins has been accomplished. The use of fractionation columns in which a temperature gradient is imposed on a solute-laden flowing stream of SCxe2x80x94CO2, either in a batch or countercurrent mode, is now being widely practiced. This methodology has been used for the production of fish oil concentrates (V. J. Krukonis et al., In: Advances in Seafood Biochemistry, G. J. Flick and R. E. Martin, Technomic Publishing Co., Basel, p. 169, 1992), fractionation of peel oil components (E. Reverchon et al., Ind. Eng. Chem. Res., Vol. 36, p. 4940, 1997), and glyceride fractionation (J. W. King, In: Supercritical Fluidsxe2x80x94Fundamentals and Applications, E. Kiran, Kluwer Academic, Dordrecht, The Netherlands, p. 451, 2000). The coupling of critical fluids with chromatography on a preparative or production scale offers another alternative route to producing nutraceutical-enriched extracts. These chromatographic-based separations range from simple displacement or elution chromatographic schemes, i.e., the removal of cholesterol (A. Shishikura et al., Agric. Biol. Chem., Vol. 50, p. 1209, 1986; R. S. Mohamed et al., J. Supercrit. Fluids, Vol. 16, p. 225, 2000), to the more sophisticated simulated moving bed technology (T. Giese et al., In: Proceedings of the International Meeting of the GVC-Fachausschuss xe2x80x9cHochdruckverfahrenstechnik,xe2x80x9d N. Dahmen and E. Dinjus, Karlsruhe, Germany, March 3-5, p. 283, 1999); the latter technique perhaps is more favored for the purification of pharmacological compounds.
Manufacture of commercially-available, phytosterol-enriched products involves isolation of free sterols from either tall oil deodorizer distillate or soybean oil. Since free sterols are not soluble in many food systems, they are esterified with fatty acids to obtain sterol esters, which have higher solubility in fats allowing them to be incorporated into the food systems as functional (cholesterol-lowering) ingredients.
We have now discovered a unique two-step (two-stage) columnar supercritical fluid fractionation process for enriching phytosterols and phytosterol esters (hereafter, xe2x80x9cphytosterolsxe2x80x9d) in vegetable oils, particularly vegetable oils containing oryzanol and/or fatty acid or ferulic esters of phytosterols. The first stage is a deacidification that utilizes a series of pressurized column zones having a thermal gradient that will minimize triglyceride (TG) and phytosterol losses. The fraction taken from the highest temperature zone (top) is rich in free fatty acids (FFA), while the product (raffinate) taken from the lowest temperature zone (bottom) is rich in phytosterol and TG. The raffinate from the first stage is introduced into the second stage (enrichment) comprising a second series of pressurized column also having a thermal gradient. The phytosterol-enriched triglyceride is taken off the second stage. (top) zone having the highest temperature of the gradient; and the raffinate from the lowest temperature zone (bottom) of the second stage is a low acidity, TG-rich edible oil.
In accordance with this discovery, it is an object of this invention to provide a method for the enrichment of phytosterols from vegetable oil sources.
It is more specific object of the invention to provide a method to enrich phytosterols in oryzanol and/or phytosterol-containing triglycerides and to simultaneously remove unwanted free fatty acids.
It is a further object of this invention to obtain enriched fractions of phytosterols, fatty acid esters of phytosterols and/or ferulic acid esters of phytosterols in a continuous or semi-continuous mode of column operation.
It is also an object of the invention to process a phytosterol-containing triglyceride using a GRAS (generally regarded as safe) solvent system and to recover product that is essentially free of residual solvent.
Another object of the invention is to enrich the phytosterol component of triglycerides by a method that is economically feasible and adaptable to industrial scale production.
Other objects and advantages of this invention will become readily apparent from the ensuing description.